Although a transmission mounted on a vehicle such as an automatic transmission in general includes a plurality of planetary gear sets and a plurality of hydraulic pressure type frictional engagement elements of a clutch or a brake and is configured to realize a plurality of forward gear shift stages and usually one stage of reverse gear shift, in recent years, as a purpose of the improvement of traveling performance and fuel economy performance of an engine or the reduction of power consumption of a driving motor, the shift shock tends to be moderated by multistaging the transmission.
To meet the requirements for multistaging and reducing weight of such an automatic transmission, a torque converter tends to be abolished, and in this case, by causing the part of the frictional engagement elements that form a first gear ratio to slip, smooth start may be realized while avoiding an engine stall. In that case, since the controllability when engaging is better for a brake in which a hydraulic chamber does not rotate compared with a clutch in which the hydraulic chamber does rotate, executing a slip control of a starting brake might be considered.
However, for conventional brakes, a fixed side friction plate is unrotatably fixed on an inner peripheral surface of a case of the transmission, in which a brake and the like are housed, and a rotation side friction plate and a rotator holding the rotation side friction plate are provided further inward in the radial direction than the fixed side friction plate.
For an automatic transmission configured like this, as the slip control executed by the start brake increases becomes more frequent and as the duration of slip control becomes longer, heating of the friction plate caused by slip needs to be suppressed effectively in order to maintain a desired durability.
To address this, it might be considered to increase the amount of lubricating oil for lubricating the start brake to thereby improve the cooling of the start brake. However, in order to increase the amount of lubricating oil that is supplied, the capacity of the pump that discharges the lubricating oil needs to be made larger, and this would result in the deterioration of fuel economy.
To address problems like these, as shown in FIG. 10 in PATENT DOCUMENT 1, a brake device 200 is disclosed that includes a rotation side holding member 202 that is rotatable and has a cylindrical shape and holds a rotation side friction plate 201, a fixed side holding member 204 that is non-rotatable and has a cylindrical shape and holds a fixed side friction plate 203 that engages and releases to the rotation side friction plate 201, and a lubricating oil supply oil passage 205 as an inflow oil passage supplying lubricating oil to the rotation side friction plate 201 and the fixed side friction plate 203. The rotation side holding member 202 includes an inner peripheral surface 204a at a position that is further outside in a radial direction than the fixed side holding member 204, and the fixed side friction plate 203 is engaged with the inner peripheral surface 204a of the fixed side holding member 204 by a spline.
A spline groove 204b on the inner peripheral surface 204a of the fixed side holding member 204 is provided so as to communicate with the inflow oil passage 205, and the lubricating oil is introduced from the inflow oil passage 205 to the spline groove 204b of the fixed side holding member 204 and moves along the spline groove 204b as shown by an arrow q. This lubricating oil then moves to the outside in the radial direction upon experiencing the centrifugal force of the rotation side friction plate 201 and is supplied between each of the friction plates 201 and 203. In this manner, during the slip control when frictional heat is generated between the rotation side friction plate 201 and the fixed side friction plate 203, each of the friction plates 201 and 203 is cooled by lubricating oil supplied from the inflow oil passage 205.